1. Technical Field
The present invention relates to a lens barrel and a projector.
2. Related Art
There is a known projector of related art that modulates light emitted from a light source in accordance with image information and projects the modulated light through a projection lens in the form of a lens barrel. The projection lens has a plurality of lens groups, and some of the lens groups are configured to be movable along the optical axis of the projection lens (see JP-A-2002-55268, for example). The projection lens is configured to change the magnification of a projected image by moving the movable lens groups.
The projection lens described in JP-A-2002-55268 includes a plurality of lens frames that hold the plurality of lens groups and have each cam pins extending outward, a cylindrical guide barrel into which the plurality of lens frames are fit and inserted, and a cylindrical cam barrel into which the guide barrel is fit and inserted. The guide barrel has open guide grooves formed along the optical axis, and the cam barrel has a plurality of cam grooves formed therein and each of the cam grooves defines movement of the corresponding lens frame. The plurality of lens frames, the cam pins of which engage with the guide grooves and the cam grooves, move along the optical axis when the cam barrel is rotated.
A method for manufacturing the projection lens described in JP-A-2002-55268 includes stacking the lens frames, supporting the stacked lens frames with a U-shaped jig (holding pin), and inserting the supported lens frames into the guide barrel all together. To carry out the manufacturing method described above, the thickness of each of the lens frames is so set that the distances between the stacked lens frames match with the distances between the cam grooves, and a hole and a groove for the supporting holding pin are provided in the outer circumferential surface of each of the lens frames.
Further, JP-A-2002-55268 discloses another technology for manufacturing the projection lens by using a holding pin provided with engaging protrusions. In the technology is characterized in that the engaging protrusions provided on the holding pin have protruding lengths different from each other in correspondence with the lens frames, and that the distances between the lens frames match with the distances between the cam grooves when the lens frames come into contact with the respective engaging protrusions.
The technology described in JP-A-2002-55268, however, has a problem of an increase in the thickness of each of the lens frames and an increase in the size of each of the lens frames in the radial direction not only because the thickness of each of the lens frames is so set that the distances between the stacked lens frames match with the distances between the cam grooves but also because each of the lens frames has a hole and a groove for the supporting holding pin. Further, a die used to manufacture each of the lens frames may undesirably have a complicated shape and a low-strength portion due to the increase in the thickness of each of the lens frames and the hole and the groove provided therein.
Further, the technology for providing the holding pin with the engaging protrusions described in JP-A-2002-55268 also has the problem of an increase in the size of each of the lens frames in the radial direction although the increase in the thickness of each of the lens frames is suppressed. As a result, each of the guide barrel and the cam barrel has an enlarged exterior shape, undesirably resulting in an increase in the size of the projection lens and an increase in the weight thereof.